Why do I get prompt for updates in MacBook Air even when it is turned off?

As user Tesserax has posted, MacOS is simply notifying you that updates are available. It's a benign and relatively minor annoyance. Never are you required to install these updates or upgrade to another version of the OS, so your music software is safe from breakage.

And, no, there really is no way to turn this off.

Also, I do hope you are backing up your computer regularly. If not, then you should be. It's easy.

Back up your Mac with Time Machine - Apple Support

Even if you’ve disabled all the visible Software Update toggles under System Settings > General > Software Update, macOS still has several underlying mechanisms designed to inform you of critical or recommended updates, especially when it comes to security or system stability. Apple considers some of these updates essential and bypasses user preferences for the sake of system integrity and ecosystem-wide security.

This includes background system services like "com.apple.softwareupdate.notifications", and Apple Security & Privacy Updates which are pushed quietly but can still trigger prompts if deferred too long. Also, even though you may have disabled automatic downloads or installations, macOS might still check periodically and then notify you when an update is available, especially if the Mac is enrolled in a beta program or has delayed updates pending.

As far as Apple required updates ... no. Apple provides you with a "right" to use macOS. As none of us actually own it, we are bound by their usage rules. This is really no different than any other operating systems, although some versions (like Linux-based) may offer more leeway with their use.

Not sure what you are getting at with your music software. If you are saying that a macOS update "breaks" your music app, it was up to the app developer to participate in the Apple Developer Beta programs. If they elected not to, could be a reason why the app does not work with a macOS update.

"Pls see image, everything is off and still get msg top right want update.: i never want update my software im using wont work if i did"

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Thank you for the screenshot.

Preventing Update Prompts:

Create a Profile:

I don't have my Mac in front of me at this moment, but, by creating a profile, you might be able to disallow updates from being installed. Would that stop the prompt? I'm not certain. Learn More Hear: Use Configuration Profiles to Standardize Settings on Mac Computers - Apple Support

It'd be similar as what I've instructed here: How to Use a Profile to Disable the iSight Camera in macOS 15 Sequoia - Apple Community

Tesserax wrote:

[...]

Not sure what you are getting at with your music software. If you are saying that a macOS update "breaks" your music app, it was up to the app developer to participate in the Apple Developer Beta programs. If they elected not to, could be a reason why the app does not work with a macOS update.

If the OP's pic is any indication, then it appears they are running an older OS - Catalina. Lots of software breaks after the change to Big Sur and newer.

This support article should answer your questions: Back up your Mac with Time Machine - Apple Support